In a thermal-sublimating dye transfer system, a recorded image is obtained by sending image information converted into electric signals to a linear type thermal printing head, and heat is generated from the back side of a dye-providing film to sublimate a dye, thereby dyeing an acceptor facing the dye-providing film with the dye.
As a material for a dye-receiving layer of the acceptor in such a heat-transfer recording system, a saturated polyester resin, polymethyl methacrylate, polybutyl methacrylate, polystyrene, an acrylonitrile-styrene (AS) resin, polyvinyl chloride, polyvinyl acetate, etc., are known. In particular, the saturated polyester resin, the acrylic resins, and the vinyl chloride resin have an excellent affinity with sublimating dyes. However, in the dye-receiving layers using these resins, the surface thereof is deformed by heating and pressing in a gap between the thermal printing heads and a rubber roller and an unevenness formed by the deformation sometimes gives an undesirable difference in the luster of the image formed.
For overcoming the problem, JP-A-62-169694 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a dye-receiving layer using a polycarbonate resin having a number average molecular weight of at least 25,000. The polycarbonate resin has an advantage that image recording having a beautiful luster without having deformation of the surface caused by heat printing heads is obtained. However, when the dye-receiving layer using the resin is formed on a base film by coating, it is necessary to use a halogenated solvent such as methylene chloride as a solvent for dissolving the resin. Hence such a method is undesirable from the standpoint of environmental pullution.
Also, a polycarbonate resin, in particular a polycarbonate resin prepared using bisphenol A as the raw material, has a disadvantage that if a solution of the resin is allowed to stand for from 3 to 4 days, the solution begins to become white turbid, and it is necessary to use the solution of the resin having a very low concentration or to re-dissolve the turbid solution for forming a dye-receiving layer by a coating method, which reduces greatly the production efficiency. On the other hand, a polycarbonate resin having a number average molecular weight of 25,000 or more has a disadvantage that since a solution of the resin is liable to become very highly viscous, it is necessary to dilute the resin solution to a low concentration of lower than 10% by weight, and preferably lower than 5% by weight, for forming a dye-receiving layer by a coating method. Hence, a large amount of a solvent must be used.